25 research outputs found
Turbulent flow and gas dispersion in stirred vessels with pseudoplastic liquids
No full textApplied Science
Turbulence spectra from laser Doppler measurements in a pseudoplastic fluid in a stirred vessel
No full textIn industry stirred vessels are often used for mixing and aerating of fluids. These fluids often exhibit Non-Newtonian behaviour. Research in stirred vessels has so far mainly been concentrated on Newtonian fluids. In this research project turbulence spectra of pseudoplastic fluids in the impeller zone of a Rushton stirred vessel were studied. The used measuring technique was Laser Doppler Velocimetry (LDV). At first the influence of noise and of the signalprocessing on the turbulence spectrum was tested. Measurements in water were conducted as a reference for Newtonian flow behaviour. The spectrum at the measuring point close to the impeller blade was dominated by periodicities. After removal of these periodicities the slope of the spectrum could be estimated using a linefit. The method used to remove the periodicities was not good enough to calculate an autocorrelation function corrected for periodicities from the spectrum. Calculation of the integral scales was therefore impossible. Due to the dominant presence of the periodic velocity component, the Taylor microscales could not be calculated either. The high frequency range of the spectrum was dominated by noise, which made measurements in the dissipation range impossible. At the measuring point close to the impeller the slopes in the spectra of the pseudoplastic fluid were comparable to those in water. At the point further from the impeller, the slopes in the pseudoplastic fluid were steeper. This was probably caused by the flow not being fully turbulent. The Reynolds number deflned according to Metzner and Otto appeared to be unsuitable to characterise the turbulence. Equal power supply will probably be a better basis to compare pseudoplastic fluids mutually and with Newtonian fluids.Kramers Laboratorium voor Fysische TechnologieApplied Science
Turbulente stroming van newtonse en niet-newtonse vloeistoffen in een geroerd vat
No full textKramers Laboratorium voor Fysische TechnologieApplied Science
Scale up of turbulent agitated vessels containing non-Newtonian liquids
No full textIn this project detailed one-dimensional Laser-Doppler measurements were carried out in two stirred vessels containing pseudoplastic, non-elastic non-Newtonian liquids. The two geometrically identical vessels were 0.441 m and 0.627 m in diameter. The flow induced by a Rushton turbine was studied in several liquids, with flow indices ranging from 0.85 to 0.57 . The effects of scale-up and pseudoplasticity on the turbulent flow were studied. Reynolds numbers of 6.0 \u95 10? up to 3.3 \u95 10?were reached. Measurements of the local instantaneous velocity components were conducted in a plane midway between two baffles, resulting in the calculation of non-dimensional mean and root mean square proflles of all three velocity components. The flow numbers and modifled flow numbers were determined at several radial positions in various liquids. It was decided not to correct the calculated flow parameters for the effect of velocity bias. A rehable, theoretically sohd correction method, applicable to all measurements conducted, was not found. All results presented are uncorrected values, allowing comparison of the measurements obtained in the two vessels, but making comparison with previously obtained results less straightforward. In addition the flow induced by an A315 axial impeller in non-Newtonian liquids, with flow indices of 0.85 and 0.72, was studied in the 0.441 m vessel, under turbulent conditions. The flow numbers and modified flow numbers at several axial positions in two different liquids were determined. The non-dimensional flow parameters in the non-Newtonian liquids were found to be independent of the impeller revolution frequency and the vessel diameter, for values of the Reynolds number of 1.0 \u95 10?or greater. The value of the flow index was found to have no significant effect on the turbulent flow parameters.Kramers Laboratorium voor Fysische TechnologieApplied Science
Apparatus and method for determining the three-dimensional shape of an object
No full textThe invention relates to an apparatus for determining a three-dimensional shape of an object from a two-dimensional image, comprising a light source for illuminating the object, and a detector for forming an image of the illuminated object, wherein the light source emits a pattern of substantially needle-like light beams that are directed at the object, and wherein the detector forms an image of spots of light of the object thus illuminated by the light beams, and a processor is connected to the detector for reconstructing the shape of the object from the image of spots of light detected by the detector.; The detector and the light source have a fixed position in relation to one another, the object is located between predetermined boundaries, and a mask is placed between the light source and the object for the formation of light rays, the mask being provided with an aperture pattern that is placed such that when the object is moved between the predetermined boundaries, the individual spots of the light spot image observed by the detector move along non-intersecting line sections.Imaging Science & TechnologyApplied Science
Critical Theories
No full textThis chapter explains how critical theories problematize the notion of great power competition because it is a state-centric one, because it grants a disproportionate role to the material aspects of power, and because it is by and large status quo affirming. For critical theorists, the global order is not simply a reflection of the distribution of material capabilities among states. Rather, power operates much more diffusely: it links different types of actors at different levels of governance and across borders. It also includes ideational components (the ability to persuade) alongside material components (the ability to force). The author shows that critical theories demand fundamental change. They do not expect it to emerge from states, and certainly not from the most powerful, because they have an interest in maintaining the status quo. Great power competition as studied by mainstream international relations theories is unlikely to truly change the global order, as it is usually part of the status quo game: international relations as we have come to expect them to work. There is a competition between elites, and it harms those most who are already disadvantaged. Critical theories therefore propose a broader framework for understanding the dynamics of competition among great powers in the international system, beyond a focus on material state power and always with an emancipatory agenda
